The present invention relates generally to a method and apparatus for making stairs, and more specifically to a bracket for use in manufacturing a step supported by a rectilinear stringer. The invented method and apparatus allow rapid, efficient, accurate, and economical construction of stairs, whether the stairs include a single step or an entire flight of steps. The invented apparatus is surprisingly adaptable to a variety of stairways, and has the unique advantage of producing steps that are incredibly quiet and squeak-free.
Conventional stairs for residential construction include a stringer made from a 2.times.12 piece of wood, with triangular portions of the stringer cut away to define the rise and run of each step. This construction requires that each triangle of removed material be marked and cut separately, involving much labor and presenting numerous opportunities for error and injury. It also results in a stringer having an effective structural thickness of only about half the thickness of the original 2.times.12 piece of lumber, with approximately one-quarter of the original 2.times.12 piece being thrown away and therefore wasted.
In the prior art, numerous attempts have been made to solve the problem of producing stairs more accurately, reliably, efficiently, and economically than the conventional 2.times.12 cut-away stringer method described above. One possible solution is to produce stairs in a factory. Through economies of scale, stairs could be pre-manufactured accurately and reliably. However, pre-manufactured stairs would be difficult to ship and install, given the significant weight and size of a completed stairs. It also would be difficult to accommodate the variables found in a typical building environment. These variables include the vertical and horizontal distance between the floors to be spanned by the stairs, and the materials to be used as the tread and riser for the stairs.
Other attempts at solving the problems of conventional construction techniques for stairs take a modularized approach. Two examples of modularized stairs are shown in U.S. Pat. Nos. 1,925,642 and 4,875,315, the disclosures of which are incorporated herein by reference. In these patents, a composite stringer is made from triangular-shaped blocks attached to a stringer of approximately 2.times.6-inches in size, using a tongue-and-groove connection. In each of these disclosures, the triangular blocks that are attached to the stringer must be cut separately if the rise or run of the stairs varies from a predetermined rise and run.
Other prior art, including U.S. Pat. Nos. 2,724,466, 4,015,687, 4,106,591, 4,635,416, 4,709,520, 4,866,894, and 5,205,093, the disclosures of which are incorporated herein, disclose various brackets for use with unaltered structural lumber or steel. However, several of these have a pre-defined rise and run for each step or, to the extent that some adjustability is allowed, are labor-intensive and unwieldy in application.
The present invention solves all of these above-identified problems. In its preferred embodiment, it includes an anchor block to which a tread for a step may be attached, a pair of frames fixed to the anchor block so that they flank the anchor block, and markings formed on at least one of the frames to indicate a rise and a run for the step. The frames are made of metal, and the anchor block is made of plastic.
To use the bracket of the present invention, a stringer is attached to span the distance required. The stringer may be of any convenient structural material, such as 2.times.6-inch lumber, or metal beams of similar size. The average rise and run of the stairs is calculated by dividing the length and height of the stairs by the number of steps to be included.
Beginning at the bottom of the stringer, a bracket for the first step is placed on the stringer and attached to define the desired rise and run. The pre-formed markings on the bracket provide a convenient, accurate and easy-to-use reference to insure that the bracket is placed at the desired settings. Successive steps are defined by attaching successive brackets in the same way, beginning at the top of the prior bracket.
If needed, the carpenter can tack several brackets in position before anchoring the brackets to the stringer, thereby allowing an empirical approach. If the calculated rise and run are found to be incorrect, adjustments then may be made prior to attaching the brackets to the stringer permanently.
With the preferred embodiment of the bracket of the present invention, both the tread and riser for each step are anchored to a plastic anchor block, and yet supported on metal frames. This has the rather surprising result of providing a step that feels very solid in use, and one that is very quiet in use. It is believed that the spaced pair of frames distributes the stresses very effectively. It also is believed that the plastic anchor block cooperates with most conventional fasteners to provide an attachment that is secure and that is very resistant to squeaking or making other noises as weight is transferred onto and off the step. For optimum results, screws such as decking screws or wallboard screws should be used.
It is an object of the present invention to provide a device that is economical to manufacture, and that may be used to make stairs accurately, efficiently, and securely.
It is a further object of the present invention to provide a method of making stairs that may be practiced by carpenters having varying degrees of skill, with consistent, high-quality results.
It is a further object of the present invention to provide a method and apparatus that reduces the amount of lumber that is wasted in the manufacturing of stairs.